A number of systems and programs are offered on the market for the design, the engineering and the manufacturing of objects. CAD is an acronym for Computer-Aided Design, e.g. it relates to software solutions for designing an object. CAE is an acronym for Computer-Aided Engineering, e.g. it relates to software solutions for simulating the physical behavior of a future product. CAM is an acronym for Computer-Aided Manufacturing, e.g. it relates to software solutions for defining manufacturing processes and operations. In such computer-aided design systems, the graphical user interface plays an important role as regards the efficiency of the technique. These techniques may be embedded within Product Lifecycle Management (PLM) systems. PLM refers to a business strategy that helps companies to share product data, apply common processes, and leverage corporate knowledge for the development of products from conception to the end of their life, across the concept of extended enterprise.
The PLM solutions provided by DASSAULT SYSTEMES (under the trademarks CATIA, ENOVIA and DELMIA) provide an Engineering Hub, which organizes product engineering knowledge, a Manufacturing Hub, which manages manufacturing engineering knowledge, and an Enterprise Hub which enables enterprise integrations and connections into both the Engineering and Manufacturing Hubs. All together the system delivers an open object model linking products, processes, resources to enable dynamic, knowledge-based product creation and decision support that drives optimized product definition, manufacturing preparation, production and service.
CAD solutions make extensive use of two main widely known technologies for surface modeling: Non Uniform Rational B-Spline surfaces (NURBS in the following) and Subdivision surfaces.
NURBS technology is based on a polynomial or rational parameterization handled by rectangular grids of 3D points, named the “control points”. Edition of a NURBS surface is performed by moving control points. The technology is designed in such a way that the degree of polynomials does not depend on the number of control points. Furthermore, the influence of control points is restricted to a neighborhood. Consequently, the user is able to locally modify the shape of the surface, the region outside of the said neighborhood being untouched. A classical reference in this field is textbook The NURBS book, L. Piegl and T. Wayne, Springer, 2nd edition, 2013.
On the other hand, a subdivision surface is defined by a 3-dimensional “base mesh” made of points and line segments. The base mesh is user-defined, and may feature an arbitrary topology, as opposed to the rectangular grid of NURBS' control points. The base mesh governs the overall shape of the subdivision surface and can be edited by the user. A change in the base mesh affects the whole subdivision surface. As opposed to NURBS surfaces, the subdivision surface is a limit object of a subdivision process starting with the base mesh. FIG. 1 illustrates a three holes closed base mesh 11 and the first subdivision steps. The limit surface is a smooth three holes-torus like object 13. The fundamentals are explained notably in the following reference: Recursively generated B-Spline surfaces on arbitrary topological meshes, E. Catmull, J. Clark, Computer Aided Design, Vol. 10, No 6, November 1978. It is noted that it is possible to approximate a subdivision surface by an arrangement of NURBS surfaces, with a conversion of the base mesh into a NURBS surface, as explained in documents U.S. Pat. No. 7,595,799 B2 (corresponding to EP 1750229 B1) and U.S. Pat. No. 7,400,323 B2.
In short, NURBS technology features a local modification capability and a grid-defined topology and Subdivision technology features an arbitrary topology and a non-local edition capability. Clearly, creation of small details on a surface while saving its overall shape is well supported by the NURBS technology because of its ability to handle local modification. Conversely, this capability is not supported by Subdivision surface technology. On the other hand, arbitrary topology is supported by subdivision surface technology as opposed to NURBS surface, the topology of which being restricted to a rectangular grid of control points.
What is missing in the prior art is notably the capability of a local change on a surface with arbitrary topology. Within this context, there is still a need for an improved solution to design a 3D modeled object.